Sonic Worlds games - framerate issue.

Not sure if this issue is in particular version of Sonic Worlds, because Chrono Adventure is unaffected. When I play Axiom, ATS or BTS, it staggers harshly (it reduces to below 20 FPS for one second) every several seconds and discourages me thus to play these games any further. I thought it is not device dependant, as it staggers in walkthrough of Razor & Zenon in YT too, until I saw Redhotsonic's video - 60 FPS intact. Is there any fix or workaround for this problem? I tried in XP and 7, both fullscreen and window mode, changed refresh rates... but it didn't work.

Those games you listed were made with an older, unoptimized version of Worlds in an older version of Multimedia Fusion 2. Stuff made with Worlds Delta shouldn't have any issues since that engine was built a lot smarter (better garbage collection, less intensive execution time, optimized code), and if it's compiled with the latest version of Fusion 2.5, it gets better performance with the runtime as well.